Is this my carb?

[cheshire190e]

Hello everyone,

I have a 1987 1.7 340 and whenever im in 5th gear and my foot is planted on the floor after a few seconds my car starts to kangaroo and then it seems like the accelerator pedal is doing nothing, you can take your foot off and then push it all the way down and nothing will happen. following this my car will cut out but then work perfectly fine again when i start it up.

Its not a major problem really i just need to go slow on the motorways but its annoying if im overtaking anything.

Anyone know what the problem could be?

just to add, one of the bolts from my carb which go through the air filter housing is missing so my carb is not a tight fit onto my air filter box, could it just be sucking in dirt, i dont see why it would only happen on full throttle though

Cheers
Matt

[Chris_C]

Not just sucking in dirt mate, more running lean whenever there is a leak. 2 of teh 3 bolts on the air filter housing you can get a niloc onto the bottom, give it a go!

[antiekeradio]

check the thermostatic valve on the air intake tube.

see if the valve lets through heated air (from exh. manifold) when it is cold, and switches over to cold air only when the wax cilinder heats up.

if it takes in cold air only, the carb may well freeze up due to condensation of moisture in the air. (evaporating fuel soaks up a LOT of heat!)

[cheshire190e]

Thanks for the advice, how exactly would i check the thermostatic valve?

also would richening the mixture up a bit help?

Cheers

[antiekeradio]

mixture at load is not determined by any settable setting

thats purely done with the jets, calibrated bores,etc.



checking of the thermo valve can be done after disassembly, with a hair dryer and/or cold water (depending on outside temperature)

[cheshire190e]

in your reply it says the carb could be freezing up. but you also say it should switch over to only cold air when the car heats up. is this right?

i would have thought it should let warm air through if it was going to freeze or am i just being stupid?

thanks

[cheshire190e]

here is a pic of the carb.

the bolt which is missing from the carb is in the bottom right. would this effect the running of the car?

[antiekeradio]

Not exactly.

What I meant to say is that the valve switches over to cold air only dependant on outside air temperature. (not dependant on engine temperature).

this means that in cold weather, a certain proportion of heated air is mixed in, irrespective of the engine temperature.


in the right conditions, the carb will freeze up even with the engine fully at 89'C

[cheshire190e]

ahh ok. so do i just aim a hair dryer at the valve? what do i have to watch for, does it move?

sorry i know nothing about this valve.

just too add too, my carb has only just had a full rebuild with new gaskets and the base was skimmed flat so thats why i thought the mixture may just be incorrectly set up.

Cheers

[Chris_C]

Take the stud (if you still have it) and chuck a nyloc on the end mate, it'll make a lot of difference. 1.7's hate airleaks around the airbox, even tiny ones.

[pettaw]

Hello, this does sound like carb icing to me. What happens is the evaporative effects of the petrol vapourising inside the carburettor can cool the air so much that it freezes inside the carb itself. The engine refuses to run properly until you stop for a minute or so, the warmth of the engine melts the ice and away you go. Cars have a heated air intake to combat this and there is a thermostatic flap inside the front of the air filter to divert warm air from the heat shield of the exhaust manifold into the air intake if temperatures fall below a certain level.

Check to make sure that your warm air hose hasn't been disconnected from the heat shield on the exhaust manifold.

[cheshire190e]

cheers guys,

the warm air pipe from the manifold is connected to the filter housing, it must be something to do with the thermostatic valve.

does anyone know how to adjust this or should i just get a new air filter box?

Cheers